The pledge came in a meeting between Alan Johnson, Trade & Industry Secretary, and Nanjing chairman Wang Haoliang, set up as part of the trade mission to China of Prime Minister Tony Blair. According to a spokeswoman for Johnson, Haoliang emphasised his company's hopes that a "substantial number of jobs" would be created.
But it would be a gradual build-up and would take time.
He insisted, she said, that Nanjing "still had a desire for a UK operation".
Nanjing has previously talked about 1,000 to 2,000 jobs in Birmingham, though it is thought no more than 1,200 are likely to materialise.
One issue discussed was intellectual property rights and discussions between MG Rover administrator PricewaterhouseCooper, Shanghai Automotive Industry Corporation - which paid £67 million to gain the blueprints to the Rover 25, Rover 75 and the K series engine - and Nanjing.
Johnson urged former workers to press on with retraining and seeking new work.
Any new job creation at Longbridge should be regarded as a "bonus", he said.
Currently plans are being drawn up between Nanjing and its UK partner, the GB Sports Car Company, which could see luxury saloon and sports car production resume at Longbridge.